A technique called “de-duplication”, which removes duplicate data at the time of storing data in a storage device in order to improve the use efficiency of a storage area, is known. For example, in this technique, when a write request of data is issued, a comparison is made of the hash value calculated based on the data and the hash value based on data that is already stored in a storage controller. If the hash values are the same, the storage controller determines that the data is duplicate data, and does not store the write-requested data in the storage device.
Related-art techniques are disclosed in Japanese Laid-open Patent Publication No. 2010-182302, and International Patent Publication No. WO 2011/121905.